Studies will be made of the light-accelerated inhibition of spinach chloroplast coupling factor (CF1) by diethylpyrocarbonate, a covalent modifier of lysine and histidine residues. The site of binding of naphthylglyoxal, a fluorescent arginine modifying reagent, will be sought. The possible existence and significance of carbohydrate residues on this enzyme will be examined. Studies of hydrogen exchange of the membrane-bound enzyme will be re-initiated, in particular to test further the concept that the energy-induced conformational change is closely related to activation of the latent ATPase.